Engines may be configured to operate with a variable number of active or deactivated cylinders to increase fuel economy, while optionally maintaining the overall exhaust mixture air-fuel ratio about stoichiometry. This operation may be referred to as VDE (variable displacement engine) operation. In some examples, a portion of an engine's cylinders may be disabled during selected conditions, where the selected conditions can be defined by parameters such as a speed/load window, as well as various other operating conditions including vehicle speed. A control system may disable selected cylinders through the control of a plurality of cylinder valve deactivators that affect the operation of the cylinder's intake and exhaust valves. By reducing displacement under low torque request situations, the engine is operated at a higher manifold pressure, reducing engine friction due to pumping, and resulting in reduced fuel consumption.
However, a potential issue with variable displacement engines may occur when transitioning between the various displacement modes, for example, when transitioning from a non-VDE (or full-cylinder) mode to a VDE (or reduced cylinder) mode, and vice-versa. As an example, a four cylinder engine that can be operated in three distinct operation modes including a full-cylinder mode, a three-cylinder mode, and a two-cylinder mode may be transitioned between the three modes in response to changes in engine loads. These transitions can significantly affect the manifold pressure, engine airflow, engine torque output, and engine power. In one example, these transitions may produce disturbances in engine torque and may increase noise, vibration, and harshness (NVH) of the engine.
The inventors herein have recognized the above issues and identified an approach to at least partially address these issues. In one example approach, a method comprises transitioning an engine with only four cylinders between two-cylinder, three-cylinder, and four-cylinder modes of operation, the transitioning including a sequence of at least two firing events, wherein the at least two firing events are successive and are separated by at least 120 crank angle degrees. In this way, operation of the four-cylinder engine may be transitioned smoothly between available modes.
In another example approach, a method comprises operating an engine in a two-cylinder mode by firing a first cylinder and a second cylinder 360 crank angle degrees apart, transitioning engine operation to a three-cylinder mode by activating a fourth cylinder and a third cylinder, deactivating the first cylinder, and firing the fourth cylinder 240 crank angle degrees after a firing event in the second cylinder. The third cylinder may be fired 240 crank angle degrees after firing the fourth cylinder to transition to three-cylinder mode.
As an example, a four-cylinder engine may be configured to operate in a two-cylinder VDE mode, a three-cylinder VDE mode, and a four-cylinder (or full-cylinder) mode. As such, three of the four cylinders may be deactivatable. The two-cylinder mode may include activating a first cylinder and a second cylinder while a third cylinder and a fourth cylinder are deactivated. Further, the first cylinder and the second cylinder may be fired at 360 crank angle degree intervals in the two-cylinder mode. The three-cylinder mode of engine operation may include deactivating the first cylinder, and activating the third cylinder and the fourth cylinder. Further, the second cylinder, the third cylinder and the fourth cylinder may be fired at evenly spaced 240 crank angle degree intervals from each other. Finally, the four-cylinder or non-VDE mode may include activating all cylinders and operating with uneven firing intervals. Herein, the first cylinder may be fired 120 crank angle degrees after a firing event in the fourth cylinder, the third cylinder may be fired 120 crank angle degrees after firing the first cylinder, the second cylinder may be fired 240 crank angle degrees after firing the third cylinder, and the fourth cylinder may be fired 240 crank angle (CA) degrees after firing the second cylinder.
Transitions between the two-cylinder mode, the three-cylinder mode, and the non-VDE mode may include activating and/or deactivating specific cylinders based on current and eventual engine operating modes. Further, the activation and/or deactivation of cylinders, as well as firing events in the activated and/or deactivated cylinders, may occur in a sequence with intervals that reduces torque disturbances.
In one example, the engine may be transitioned from two-cylinder mode to four-cylinder mode by activating the third cylinder and the fourth cylinder. A smoother transition may be achieved by activating the third cylinder earlier than the fourth cylinder and timing a transition sequence as follows: activation of the third cylinder followed by a firing event in the second cylinder, firing of the first cylinder 360 CA degrees after the firing event in the second cylinder, activation of the fourth cylinder, firing of the third cylinder 120 CA degrees after the firing event in the first cylinder, firing of the second cylinder 240 CA degrees after firing the third cylinder, and firing of the fourth cylinder 240 CA degrees after firing the second cylinder. Herein, the sequence of five successive firing events includes a firing interval of at least 120 CA degrees between at least two successive firing events.
In another example, engine operation may be transitioned from two-cylinder mode to three-cylinder mode by simultaneously activating the fourth cylinder and the third cylinder. Next, the first cylinder may be deactivated following a last firing event in the first cylinder. The second cylinder may be fired 360 CA degrees after the last firing event in the first cylinder, the fourth cylinder may be fired 240 CA degrees after firing the second cylinder, and the third cylinder may be fired 240 CA degrees after firing the fourth cylinder. Herein, the sequence of firing events in the transition may include successive firing events that occur at an interval of 240 CA degrees (at least 120 CA degrees or greater).
In this way, engine operation may be transitioned between three available modes to reduce torque disturbances. By scheduling transitions such that firing events during the transition phase occur at specific intervals, a smoother transition with reduced NVH may be attained. Fuel consumption may also be decreased by enabling timely transitions. Further, by reducing perceptible NVH, passenger comfort may be improved. Overall, engine operation and drivability may be enhanced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.